1. Field of the Invention
The present invention relates to a variable geometry exhaust turbocharger configured such that the angle of nozzle vanes can be changed.
2. Description of the Related Art
Conventionally, in a relatively small-sized turbocharger which is used for a vehicle internal combustion engine or the link, exhaust gas from the engine fills a scroll formed in a turbine housing, is fed through a plurality of nozzle vanes arranged on an inner peripheral side of the scroll, and is then applied to a turbine rotor arranged on the inner peripheral side of the nozzle vanes. And a variable nozzle mechanism which is capable of changing the blade angle of the plurality of nozzle vanes, is used. A variable geometry exhaust turbocharger of radial flow type which is equipped with the variable nozzle mechanism has been often used. For example, this type of the variable nozzle mechanism is illustrated in Patent Documents 1 to 3.
FIG. 5 shows a conventional example of the exhaust turbocharger incorporating the abovementioned variable nozzle mechanism. This figure is a sectional view taken along the rotating axis thereof. FIG. 5 shows a turbocharger having a turbine housing 1 which has a thick multi-cylindrical shape. A scroll 2 is formed in a spiral-like configuration on the outer peripheral side of the turbine casing 1. On the inner peripheral side of the turbine housing, a turbine rotor 3 of a radial flow type is provided. The turbine rotor 3 is mounted on a turbine shaft 3A which has a rotation axis K and is arranged coaxially with a compressor. The turbine shaft 3A is rotatably supported in a bearing housing 4 via a bearing 5.
A concave portion of an annular shape is formed on a rear face of the bearing housing 4. In the concave portion, housed is a variable nozzle mechanism 8 having a nozzle 6, a nozzle mount 7 and so on. Herein, a plurality of nozzles 6 is provided around the rotation axis K at equal intervals. Further, the nozzles 6 are located on the inner peripheral side of the scroll 2 in the radial direction of the turbine. Each of the nozzles 6 comprises a nozzle vane 6a and a nozzle shaft 6b. The nozzle shaft 6b is rotatably supported in the nozzle mount 7 secured to the bearing housing 4. And the blade angle of the nozzle vanes can be changed by the variable nozzle mechanism 8.
The nozzle vanes 6a are arranged between the nozzle mount 7 and an annular nozzle plate 9 which is coupled to the nozzle mount 7. The nozzle plate 9 is attached to a tip portion of an inner cylindrical portion of the turbine housing 1.
The nozzle mount has an elevated portion on a front face thereof. On the elevated portion, a drive ring 10 which is formed in a disc-like shape is rotatably supported. A lever plate 11 is engaged with the drive ring 10. The lever plate 11, whose enlarged view is shown in FIG. 6, comprises a bent portion 11a and a protruding portion 11b for engagement. The protruding portion 11b for engagement is engaged in a groove 10a of the drive ring 10.
Further, the lever plate 11 has through-holes formed along the rotation axis K on the inner peripheral side of the lever plate. A fixed part 6c formed on the tip side of the nozzle shaft 6b is inserted in the through-hole.
FIG. 7 is shows an elevation from the direction A of FIG. 6. As shown in the figure, the drive ring 10 is arranged closer to the center of the radial direction on the disk-shaped nozzle mount 7. On the drive ring 10, the lever plates 11 are connected. The fixed parts 6c of the nozzles 6 are engaged in the lever plate 11 on the rotation shaft K side thereof. The figure shows twelve lever plates provided around the rotation shaft K. The opening of the nozzles 6 are adjusted by rotating the drive ring 10.
During the operation of the variable geometry type exhaust turbocharger incorporating the variable nozzle mechanism having the configuration explained through FIG. 5 to FIG. 7, exhaust gas from an engine (not shown in the drawings) is led into the scroll 2 so as to be swirled along spiral passages in the scroll 2, and is then introduced through the nozzle vanes 6a. Then the exhaust gas flows through the gaps between the vanes and then flows onto the turbine rotor 3 from the outer periphery of the turbine rotor 3. Thereafter, the exhaust gas flows radially toward the center of the turbine rotor 3 so as to carry out the expansion to the turbine rotor 3. Then, the exhaust gas flows along the axial direction, and is led to a gas outlet from which the exhaust gas is discharged to outside of the turbocharger.
To control the delivery volume of the above-mentioned variable geometry type exhaust turbocharger, the blade angle of the nozzle vanes 6a is set by an blade angle controller (which is not shown) so as to regulate the flow rate of the exhaust gas passing through the nozzle vanes 6a to a desired rate. The reciprocal displacement of the actuator in response to the thus set blade angle is transmitted to the drive ring 10 so as to rotate the drive ring 10.
The rotation of the drive ring 10 causes the lever plates 11 to rotate around the nozzle shaft 6b via the protruding portions 11b which are engaged in the grooves 10a formed in the drive ring 10. The rotation of the nozzle shafts 6b causes the nozzle vanes 6a to rotate so as to change the blade angle of the nozzle vanes 6a. 